test2991.c

#include <stdio.h>

typedef struct Foo_t {
  int a;
  char * s;
} Foo;

void my_func (Foo  foo) {
  fprintf (stdout, "a: %i, s: %s\n", foo.a, foo.s);
}

void my_func2 (Foo * foo) {
  fprintf (stdout, "a: %i, s: %s\n", foo->a, foo->s);
}

int main (char * argv, size_t argc) {
  // This does work
  my_func ((Foo) {10, "World!"});

  // This does not work.
  my_func2 ((Foo *) {5, "Hello!"});
  return 0;
}